Soriano had worked at Barcelona six months after Van Gaal's second stint at the Camp Nou ended and, addressing a football management seminar in March, he said the current Netherlands boss had a habit of making enemies wherever he went.

The Times reported him as saying: "If you treat your people badly, they remember. One day you make an error and they kill you. I've seen this in many clubs.

"Louis van Gaal has been a very good coach in many clubs but his style is very difficult. The same thing happened to him in Barcelona as in Bayern Munich. He is very tough, people don't like him, but he wins. And one day you don't win -- and when you don't win, everybody that is angry with you will come back to you and try to kill you.

"In the movies, this works; in real life, it doesn't."

Van Gaal has since entered into negotiations with United over the prospect of succeeding David Moyes, and it is expected that it will soon be confirmed that he will take charge following the World Cup this summer.

However, he has also had several high-profile disagreements during his managerial career, and Soriano wrote in his book "Goal: The Ball Doesn't Go In By Chance" that Van Gaal was a good example of an "authoritarian expert" -- described as those who "do not accept their mistakes, they try not to pay attention to them, and brush them aside as quickly as possible."

On the Dutchman, he added: "He has won titles with different teams, big and small, and he's thought to have little empathy and social skills. I couldn't help but smile when I heard Uli Hoeness, then Bayern Munich's technical director, explain why Van Gaal wouldn't continue to coach the Bavarian team: 'Van Gaal doesn't listen, it has to be whatever he said.' It seems his reputation is justified."